1. Field of the Invention
The present invention relates to a document reading apparatus that reads out a document placed on a document positioning plate while moving a frame member onto which a reading element is held.
2. Description of the Related Art
Conventional image reading apparatus includes a platen glass on which a document is placed, alight source that illuminates a light on the document, a lens that causes a diffused light from the document to form an image, an image reading element such as a charge coupled device (CCD) that reads out an image-formed light, and an electric board for driving the image reading element. Then, a positional relationship among the platen glass, the lens, and the image reading element is adjusted, during assembly of the image reading apparatus, and the lens and the reading element are fixed to other member so that the positional relationship between the lens and the image reading element may not deviate.
FIG. 5 illustrates a scanning unit of the image reading apparatus, using an integrated optical system that integrally holds a light source 501, a lens 502, an image reading element 503, and an electric board 504, and scans a document. The scanning unit is configured such that the image reading element 503 and the electric board 504 are fixed to the holding member 505 located between the image reading element 503 and the electric board 504. Then, end portions of the holding member 505 are fixed to a carriage frame member by soldering.
Further, Japanese Patent Application Laid-Open No. 2001-245098 discusses a method for fixing a spacer which holds the CCD and the electric board with screw-fixing only in the vicinity of the CCD. In the scanning unit illustrated in FIG. 5, the end portions of the holding member are fixed by soldering. Consequently, when the electric board and the image reading element generate heat during scanning operation, the holding member will expand due to the heat, and the holding member will suffer warpage. When the warpage occurs in the holding member, the position of image reading element relative to the lens will be shifted, and focus or magnification will be shifted.
Further, in the method discussed in Japanese Patent Application Laid-Open No. 2001-245098, since the end portions of the electric board are not fixed, vibration occurs when an integrated optical system to which the CCD has been fixed is moved to scan a document. Then, a position of the CCD will be minutely changed due to the vibration. There is a possibility that defects may occur such that jitter occurs on the read-out image.